1. Field of the Invention
The present invention relates to a process for manufacturing a printed circuit board, including a flexible type as well as a plate type.
2. Brief Description of the Prior Art
The development of semiconductor circuit techniques has generalized and necessitated the use of printed circuit boards as components of electronic devices or instruments. Conventional procedures of manufacturing printed circuit boards include the steps of forming a coat of a pre-flux for the protection of the circuit surfaces, mounting electronic parts on the printed circuit boards, forming a coat of a post-flux, and soldering. These fluxes contain gum rosin, wood rosin, modified rosin or the like as a major component dissolved in an alcohol, an ester, a ketone, an aromatic hydrocarbon, water or the like. The flux coats are applied in a liquid form by the following procedures: with a brush or with a roller; in a flux solution or in a bubbling flux solution for immersion; or by spraying.
These coating methods, however, present serious problems in that nonuniformity of the coats is encountered, the stability of the soldering and the function of the electronic parts are impaired because the solution of the flux will pass through inserting holes for lead wires into the non-coated surface side and penetrate into the inside thereof along the lead wires of the mounted electronic parts. Where an organic solvent of the alcohol or aromatic hydrocarbon type is employed, the flux coating step which is conducted immediately prior to the soldering step to be carried out at a high temperature causes other problems in that there is an increased risk of fire, and storage should be effected in accordance with rules and regulations related to handling dangerous materials.